Procatalyst composition containing substituted maleic or fumaric acid esters as an electron donor for olefin polymerization

ABSTRACT

It is known that an electron donor together with a compound of tetravalent titanium on a magnesium halide carrier is usable if it is a mono- or polyester of an unsaturated polycarboxylic acid in which at least two carboxyl groups are joined to contiguous carbon atoms which form double bonds. It has now been observed that activity and stereospecificity increase if at least one of the said carbon atoms, or a carbon atom joined thereto by a double bond, is substituted by a hydrocarbon group having 1-20 carbon atoms. Maleic and fumaric acid esters substituted with the said hydrocarbon group can be mentioned as examples.

FIELD OF THE INVENTION

The invention relates to a procatalyst composition for an α-olefinpolymerization catalyst, the composition comprising a magnesium dihalidecarrier and thereon a compound of tetravalent titanium and an electrondonor, the electron donor being a mono- or polyester of an unsaturatedpolycarboxylic acid in which at least two carboxyl groups are joined tocontiguous carbon atoms which form double bonds.

BACKGROUND OF THE INVENTION

α-olefins are often polymerized using a Ziegler-Natta catalyst systemmade up of a so-called procatalyst and a cocatalyst. Of these, theprocatalyst component is based on a compound of a transition metalbelonging to any of Groups IVA-VIII in the Periodic Table of theElements, and the cocatalyst component is based on an organometalliccompound of a metal belonging to any of Groups IA-IIIA in the PeriodicTable of the Elements (the groups are defined according to Hubbard, i.e.IUPAC). The catalyst system may also include a carrier on which thetransition-metal compound is deposited and an internal electron donorwhich enhances and modifies the catalytic properties and is deposited onthe carrier together with the transition-metal compound. In addition, aseparate so-called external electron donor can also be used togetherwith the procatalyst and the cocatalyst.

In the preparation of stereoselective high-yield Ziegler-Natta catalystson a magnesium dihalide, organic esters are widely used as internaldonors to improve the said properties of the catalyst. Publications U.S.Pat. No. 4,522,930, EP-45 977 and FI-70 028 describe an α-olefinpolymerization catalyst obtained by causing a cocatalyst, an externaldonor and a carrier-based procatalyst to react together. The procatalystis made up of a titanium compound deposited on a magnesium dihalidecarrier and of an internal electron donor. The internal donor may be anyof the following (summary of the above state of the art):

1) saturated dicarboxylic acid ester,

2) unsaturated polycarboxylic acid ester,

3) aromatic di- or polycarboxylic acid ester,

4) aromatic oligohydroxy compound ester,

5) monocarboxylic acid ester,

6) araliphatic polycarboxylic acid ester,

7) heterocyclic aromatic polycarboxylic acid ester,

8) carbonic acid ester,

9) polyol or monohydroxyphenol ester,

10) acetylenic acid ester.

Regarding group 2) it is stated that the two carboxyl groups may, or maynot, be linked to contiguous carbon atoms which form double bonds. As anexample of internal electron donors of the former type, publicationsFI-70 028 and EP-45 977 mention the compounds di-2-ethyl-hexyl maleate,di-isobutyl maleate, di-isobutyl-3,4-furan-dicarboxylate,di-2-ethyl-hexyl fumarate, 2-ethyl-hexyl fumarate, and 2-ethyl-hexylmonomaleate. In addition, the FI publication states that the esters ofmaleic, pivalic, carbonic, and phthalic acids are especiallyadvantageous internal donors.

According to Table I of the FI and EP publications, the activity ofmaleates is, however, only about one-half of the activity of phthalates,and thus there is very little use for them in commercial processes. Bythe same criteria it can be concluded that the di-butyl-itaconatepresented in the table of the US publication is not a practicableinternal donor, either.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a maximally activeprocatalyst composition for a polymerization catalyst. The invention atthe same time aims at a procatalyst composition which yields a maximallytactic polymer. A further aim is that the polymer produced should have asuitable morphology, bulk density, and melt index.

These objectives have now been achieved with a procatalyst combinationfor an α-olefin polymerization catalyst, the procatalyst combinationbeing is primarily characterized in what is stated in thecharacterization clause of claim 1. It has thus been realized that, ifthe electron donor used is a mono- or polyester of an unsaturatedpolycarboxylic acid in which at least two carboxyl groups are joined tocontiguous carbon atoms forming double bonds, at least one of the saidcarbon atoms of the electron donor, or a carbon atom joined thereto by adouble bond, is to be substituted by a hydrocarbon group having 1-20carbon atoms.

The invention is thus based on the surprising observation thathydrocarbon groups in the vicinity of the carboxyl groups and doublebonds in unsaturated polycarboxylic acids have a greatly increasingeffect on catalyst activity.

DETAILED DESCRIPTION OF THE INVENTION

The procatalyst composition according to the invention comprises amagnesium dihalide carrier and thereon a compound of tetravalenttitanium and an electron donor. The magnesium dihalide carrier ispreferably magnesium dichloride. The tetravalent titanium compound maybe a titanium alkoxide, a titanium alkoxide halide, or a titaniumhalide. Preferably it is titanium tetrachloride.

According to one preferred embodiment, the magnesium dihalide carrierand the compound of tetravalent titanium and the electron donor thereonare prepared by melting magnesium dichloride together with a loweralcohol, such as ethanol, and possibly an internal donor, to produce amolten homogeneous mixture, which is then formed by physical means intosmall active particles of carrier material. Substantially sphericalcarrier particles can, for example, be prepared by spray-crystallizingthe said melt in accordance with U.S. Pat. No. 4,829,034.

Thereafter the carrier particles are activated by contacting them with acompound of tetravalent titanium and possibly at this stage also with aninternal donor. Often a repeat treatment with the compound oftetravalent titanium is carried out in order to produce a maximallyactive procatalyst.

As stated above, in the electron donor at least one of the carbon atomsforming double bonds or joined thereto by a double bond is substitutedby a hydrocarbon group having 1-20 carbon atoms. In this case it isadvantageous if the electron donor is a maleic or fumaric acid estersubstituted with the said hydrocarbon group. According to one preferredembodiment, the electron donor is a maleic acid diester monosubstitutedwith the said hydrocarbon group. In this case it is most preferable thatit is dialkyl cis-2-methyl-butenedioic acid ester with 1-10 carbon atomsin its alkyl. Some such compounds are:

DEMB=diethyl cis-2-methyl-butenedioic acid ester,

DIBMB=di-isobutyl cis-2-methyl-butenedioic acid ester,

DDMB=didecyl cis-2-methyl-butenedioic acid ester.

It has been observed that a procatalyst composition according to theinvention works very well if its electron donor/magnesium molar ratio iswithin a range of approx. 0.050-0.50. Its Al/Ti molar ratio ispreferably within a range of approx. 500-1000, and its Al/electron donormolar ratio is preferably within a range of approx. 10-30. Thepreparation of catalysts according to the invention and their use forthe polymerization of propylene are described in the following examples.The steps of catalyst preparation are identical in all the examples,unless otherwise indicated. There are 6 embodiment examples and 4comparison examples, namely BCDE. The purpose of the comparison examplesis to make a comparison between nonsubstituted unsaturated diesters,such as dialkyl maleates, and substituted unsaturated diesters accordingto the present invention.

The following abbreviations are used in the examples and the tables:

DEMB=diethyl cis-2-methyl-butenedioic acid ester,

DIBMB=di-isobutyl cis-2-methyl-butenedioic acid ester,

DDMB=didecyl cis-2-methyl-butenedioic acid ester,

DEME=diethyl maleate,

DIBME=di-isobutyl maleate,

DDME=didecyl maleate.

EXAMPLE 1

Activation of a MgCl₂ *3EtOH carrier was performed as follows:

24.5 g of the above-mentioned carrier, prepared in accordance with U.S.Pat. No. 4,829,034, is added at -10° C. into a vessel containing 150 mlof heptane and 300 ml of TiCl₄. The carrier is allowed to react whilethe temperature is raised slowly to +20° C., with mixing. At thistemperature, 1.9 ml of DIBMB is added, i.e. the DIBMB/Mg molar ratio is0.075, and the temperature is raised within 60 minutes to +110° C. andis maintained at that level for 60 minutes. The treatment is repeatedwith 300 ml of TiCl₄ at +120° C. for 60 minutes. The product is washedwith 300 ml of heptane at 80° C. for 20 minutes. The washing is repeatedfive times, and the product thus obtained is dried in a nitrogen streamat room temperature.

The dried procatalyst was brown, and the following analytical resultswere obtained regarding it:

Ti 3.1% by weight; Mg 16.7% by weight; Cl 58.0% by weight; DIBMB 9.7% byweight; heptane 12.5% by weight.

The polymerization was carried out in a two-liter autoclave by using 900ml of heptane as the medium:

P(C₃ H₆)=7 bar

AlEt₃, 5 mmol; Al/Ti=737

P(H₂)=0.3 bar

Al/electron donor=20

T=+70° C.

Catalyst quantity=25.0 mg

t=4 h

Triethyl aluminum was used as the cocatalyst andcyclohexyl-methyl-dimethoxysilane was used as the electron donor. Theactivity of the catalyst was 529 kg polypropylene per g Ti and 18.7 kgPP/g dry catalyst.

The evaporation residue obtained from the polymerization fluid was 0.7%by weight, calculated from the total polypropylene quantity. Theisotacticity of the polypropylene was 97.2%, its isotactic index 96.5%,and its relative density 0.47 g/cm³. The melt index of the polymer was6.2 g/10 min (see Tables 1 and 2 ).

EXAMPLES 2-4

The preparation of the catalyst was performed exactly as in Example 1 byusing the carrier mentioned above, but the DIBMB/Mg molar ratios were0.125, 0.175 and 0.350 (in examples 2, 3 and 4, respectively). Theanalytical results of the catalysts are shown in Table 1.

Propylene polymerization was performed as in Example 1 (25.0 mg ofprocatalyst, 5 mmol of AlEt₃ and an Al/electron donor molar ratio of 20were used). The results of the polymerization are shown in Table 2.

EXAMPLE 5

The preparation of the catalyst was performed exactly as in Example 1 byusing the carrier mentioned above, but DEMB was used instead of DIBMB asthe internal donor. The DEMB/Mg molar ratio in the procatalyst synthesiswas 0.075. The analytical results of the procatalysts obtained are shownin Table 1.

Propylene polymerization was performed as in Example 1 (25.0 mg ofcatalyst, 5 mmol of AlEt₃, and Al/electron donor molar ratio 20). Thepolymerization results are shown in Table 2.

EXAMPLE 6

The preparation of the catalyst was performed exactly as in Example 1 byusing the carrier mentioned above, but DDMB instead of DIBMB was used asthe electron donor. The DDMB/Mg molar ratio in the procatalyst synthesiswas 0.104. The analytical results of the procatalysts are shown in Table1.

Propylene polymerization was performed as in Example 1 (25.0 mg ofprocatalyst, 5 mmol of AlEt₃, and Al/electron donor molar ratio 20). Thepolymerization results are shown in Table 2.

COMPARISON EXAMPLE A

The preparation of catalyst was performed exactly as in Example 1, byusing the same carrier, but no electron donor was used. The analyticalresults were: Ti 7.2% by weight; Mg 14.2% by weight; Cl 57.2% by weight;heptane 21.4% by weight.

Propylene polymerization was performed as in Example 1. The activity ofthe catalyst was 149 kg polypropylene per g Ti. The evaporation residuefrom the polymerizing fluid was 15.3% by weight, calculated from thetotal polypropylene quantity obtained. The isotacticity of thepolypropylene was 91.7% and its isotactic index 77.7%. Specific densitywas not measured, since the polypropylene was sticky owing toamorphousness. The melt index of the polymer was 3.0 g/10 min.

COMPARISON EXAMPLES B, C, D AND E

The preparation of the catalyst was performed exactly as in Example 1,by using the same carrier, but di-isobutyl maleate (DIBME) instead ofDIBMB was used as the internal donor. The DIBME/Mg molar ratios were0.075, 0.125, 0.175, and 0.350. The analytical results of theprocatalysts obtained are shown in Table 1. Propene polymerization wasperformed as in Example 1, and the polymerization results are shown inTable 3.

                  TABLE 1                                                         ______________________________________                                        Type and quantity of the donor used in synthesis,                             and analytical compositions of the catalysts (in % by weight)                         Donor/Mg  Donor/ml                                                    Example molar ratio                                                                             added     Ti  Mg   Cl   Donor                               ______________________________________                                        1       0.075     DIBMB     3.1 16.7 58.2 9.7                                                   1.9                                                         2       0.125     DIBMB     2.4 18.5 61.2 7.5                                                   3.2                                                         3       0.175     DIBMB     2.2 15.9 53.0 9.1                                                   4.5                                                         4       0.35      DIBMB     5.7 15.1 61.0 23.0                                                  8.9                                                         5       0.075     DEMB      1.7 15.9 51.5 10.7                                                  1.5                                                         6       0.104     DDMB      3.1 16.8 58.3 13.8                                                  4.4                                                         Comp. B 0.0750    DIBME     2.2 12.9 56.2 5.4                                                   1.8                                                         Comp. C 0.125     DIBME     2.5 16.7 56.2 8.3                                                   3.1                                                         Comp. D 0.175     DIBME     2.5 17.8 59.4 9.6                                                   4.4                                                         Comp. E 0.35      DIBME     5.7 11.9 51.7 21.5                                                  8.8                                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Performance of the catalysts in propylene                                     polymerization carried out in a heptane slurry by                             using internal donors in accordance with the invention                                        Activity                                                                      in kg                                                                Activity PP/g of  Isotacticity/                                               in kg    dry cat- evaporation                                                                            I.I.                                        Example                                                                              PP/g Ti  alyst    residue  (%)  B.D. M.I.                              ______________________________________                                        1      529      18.7     97.2/0.7 96.5 0.47 6.2                               2      592      16.1     98.2/0.7 97.5 0.39 8.5                               3      595      16.3     98.3/0.6 97.7 0.37 12.5                              4      204      11.6     98.7/0.7 98.0 0.41 12.0                              5      876      18.7     98.6/1.1 97.5 0.39 2.2                               6      574      19.5     95.8/0.9 94.9 0.43 6.3                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Performance of procatalysts in propylene                                      polymerization carried out in a heptane slurry using                          as the internal donor DIBME, a compound in accordance                         with the state of the art                                                                     Activity                                                                      in kg                                                                Activity PP/g of  Isotacticity/                                               in kg    dry cat- evaporation                                                                            I.I.                                        Example                                                                              PP/g Ti  alyst    residue  (%)  B.D. M.I.                              ______________________________________                                        Comp. B                                                                              559      12.3     97.1/1.3 95.8 0.45  8.0                              Comp. C                                                                              372      9.3      97.1/1.1 96.0 0.40 14.4                              Comp. D                                                                              147      6.0      97.7/1.4 96.3 0.39 14.1                              Comp. E                                                                               37      1.6      96.8/7.0 89.8 0.31 13.0                              ______________________________________                                    

We claim:
 1. A procatalyst composition for an α-olefin polymerizationcatalyst, the procatalyst composition comprising a magnesium dihalidecarrier and, thereon, a compound of tetravalent titanium and an electrondonor, the electron donor being selected from the group consisting ofdiethyl cis-2-methyl-butenedioic acid ester, diisobutyl cis-2-methylbutenedioic acid ester and didecyl cis-2-methyl-butenedioic acid ester.2. A procatalyst composition according to claim 1, characterized in thatthe magnesium dihalide carrier is magnesium dichloride.
 3. A procatalystcomposition according to claim 2, characterized in that the magnesiumdichloride carrier is prepared by melting dry magnesium chloride andethanol together, by forming from the melt small drops, and bysolidifying the melt drops by cooling, preferably by spraycrystallization, to form solid carrier particles.
 4. A procatalystcomposition according to claim 1, 2 or 3, characterized in that thecompound of tetravalent titanium is titanium tetrachloride.
 5. Aprocatalyst composition according to claim 1, 2 or 3, characterized inthat its electron donor/magnesium molar ratio is within a range ofapprox. 0.01-0.50.
 6. A procatalyst composition according to claim 1, 2or 3, characterized in that the polymerization catalyst in which it is acomponent also comprises an organometallic aluminum compound as acocatalyst and, electively, an external donor.
 7. A procatalystcomposition according to claim 6, characterized in that theorganometallic aluminum compound is trialkyl aluminum, preferablytriethyl aluminum, and the external donor is dimethyl-dialkoxysilane,preferably cyclohexyl-methyl-dimethoxysilane.
 8. A procatalystcomposition according to claim 6, characterized in that the Al/Ti molarratio is within a range of approx. 1-1000, preferably approx. 500-1000.9. A procatalyst composition according to claim 6, characterized in thatthe Al/electron donor molar ratio is within a range of approx. 0.1-200,preferably within a range of approx. 10-30.